1. Field
An air conditioner and a method for controlling an air conditioner are disclosed herein.
2. Background
Air conditioners are home appliances that maintain indoor air in a most proper state according to a use and purpose thereof. In general, such an air conditioner may include a compressor, a condenser, an expansion device, and an evaporator. Thus, the air conditioner has a refrigerant cycle in which compression, condensation, expansion, and evaporation processes of a refrigerant are performed to cool or heat a predetermined space.
The predetermined space may be a place at or in which the air conditioner is used. For example, when the air conditioner is disposed in a home or office, the predetermined space may be an indoor space of a house or building. On the other hand, when the air conditioner is disposed in a vehicle, the predetermined space may be a riding space in which a person or user rides.
When the air conditioner performs a cooling operation, an outdoor heat-exchanger provided in an outdoor unit or device may serve as a condenser, and an indoor heat-exchanger provided in an indoor unit or device may serve as an evaporator. On the other hand, when the air conditioner performs a heating operation, the indoor heat-exchanger may serve as a condenser, and the outdoor heat-exchanger may serve as an evaporator.
An inner temperature of the compressor may increase to a relatively high temperature while the compressor compresses the refrigerant. A predetermined amount of oil to provide lubrication and cooling functions may be included in the compressor. However, as described above, when the inner temperature of the compressor increases to the relatively high temperature, the oil in the compressor may be included in the refrigerant being discharged. Thus, an amount of the oil in the compressor may be reduced or decline.
Therefore, an oil separator may be connected to a discharge tube of the compressor to separate the oil included in the discharged refrigerant and re-collect the separated oil into the compressor. When a plurality of compressors is provided, the oil separator may be connected to an outlet-side of each of the compressors.
However, when the oil separator is connected to the outlet-side of each of the plurality of compressors, an amount of oil received in each of the plurality of compressors may not be uniform. That is, when the plurality of compressors has different capacities from each other, and thus, discharge different amounts of refrigerant, amounts of oil being discharged may be different from each other. Thus, amounts of the oil in the plurality of compressors may be imbalanced or different from each other. Also, when a compressor operates in a state in which an amount of oil therein is non-uniformly maintained, the compressor may break, and thus, a cooling/heating system employing the compressor may operate abnormally.
FIG. 1 is a schematic diagram of a plurality of compressors in a related art air conditioner. FIG. 2 is flow chart of a method for controlling oil balancing in the related art air conditioner of FIG. 1.
Referring to FIGS. 1 and 2, the related art air conditioner includes a first compressor 11 and a second compressor 12. A first inflow tube 13 to guide introduction of a refrigerant or oil into the first compressor 11 and a first discharge tube 14 to guide the refrigerant or oil discharged from the first compressor 11 may be connected to the first compressor 11. A second inflow tube 15 to guide introduction of the refrigerant or oil into the second compressor 12 and a second discharge tube 16 to guide the refrigerant or oil discharged from the second compressor 12 may be connected to the second compressor 12.
The first and second inflow tubes 13 and 15 are branched at a branch point 22, and the branched first and second inflow tubes 13 and 15 are, respectively, connected to the compressors 11 and 12. Also, the first and second discharge tubes 14 and 16 are combined with each other at a combination point 21.
A first oil level sensor 17 and a second oil level sensor 18 may be disposed in or at the first and second compressors 11 and 12, respectively. Each of the oil level sensors 17 and 18 may detect an amount of oil at a predetermined position in the respective compressor.
Referring to FIG. 2, when the first and second compressors 11 and 12 operate at a set or predetermined drive frequency, a predetermined amount of oil may be introduced into the first and second compressors 11 and 12 in accordance with the corresponding drive frequency, in step S11. A control number N is initialized to zero, in step S12. In step S12, the control number N may be understood as a number of control operations performed to reduce the drive frequency of the first compressor 11.
In steps S13 and S14, the first oil level sensor 17 detects an amount of oil contained in the first compressor 11 and determines whether the detected oil amount is less than a reference amount. When it is determined that the detected oil amount is less than the reference amount, it may be determined whether the controlled number N has reached a first set or predetermined number M, in step S15. When N<M, the first compressor 11 may perform a control to reduce the drive frequency and then operate for a preset or predetermined time, in step S16. Also, the control number N is increased by 1 (N=N+1), in step S17. Then, the process may return to step S13. Steps S13 to S17 may be repeated.
During the process, in steps S16, when it is determined that N=M, the first and second compressors 11 and 12 operate at a normal frequency. That is, in the related art, when an amount of oil contained in one compressor of the plurality of compressors is less than the reference amount, the corresponding compressor is reduced in drive frequency to reduce a discharge amount of refrigerant, and then, a relatively large amount of refrigerant is discharged from the rest of the compressors to adjust the amount of oil contained in the refrigerant.
Therefore, as it takes a lot of time to collect the oil, oil balancing may not be quickly achieved.